The three isomers of dimethylbenzene are commonly named ortho-xylene, meta-xylene, and para-xylene. These three isomers are difficult to distinguish using proton NMR, but they are instantly identifiable using 13C NMR.

(a) Describe how carbon NMR distinguishes these three isomers.
(b) Explain why they are difficult to distinguish using proton NMR.

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CH3 CH3 CH3 CH3 CH3 I HC meta-xylene para-xylene ortho-xylene 1,2-dimethylbenzene 1,3-dimethylbenzene 1,4-dimethylbenzene